1. Field of the Invention
The present invention relates to a plasma treating method and apparatus therefor, and more particularly to a plasma treating method and apparatus therefor which is suitable for the treatment of a specimen such as the substrate of a semiconductor device (hereinafter termed as `wafer`) with a plasma.
2. Description of the Prior Art
As a conventional plasma treating apparatus such that a magnetic field is introduced to improve the efficiency of generating a plasma and increase a treating rate, there is well known one by which the treatment is performed particularly with a magnetron discharge generated.
Most of the voltage inside a sheath to be formed on the electrodes for a glow discharge to be generated by using a direct current or a radio-frequency power supply turns out to have an electric field formed perpendicularly to the electrodes. A magnetron discharge is generated by imposing to such an electric field a magnetic field intersecting the electric field orthogonally. Inside the sheath with the electric and magnetic fields intersecting orthogonally, electrons perform a cycloidal motion and the motion of electrons along the direction of the electric field is restricted to a narrow range.
The plasma treating apparatus for the treatment by generating such a magnetron discharge has the following drawbacks.
A first drawback consists in uniformity of the distribution of a treating rate over a full area on the wafer. The intensity of a magnetron discharge depends upon a vector product of an electric field vector E and a magnetic field vector B , 1 .times. 1, and a magnitude of the magnetic field vector 1 should be set so that an amplitude in the direction of the electric field when electrons perform the cycloidal motion will be substantially as large as the thickness of the sheath. But, in fact, a scattering of electrons as the result of the collisions between electrons and molecules inside the sheath prevents accomplishment of providing a sufficient effect in converting into a plasma, and, then, a much higher intensity of the magnetic field than should be necessary at such a time will be required. However, it is impossible to obtain such a magnetic field having uniformity through a full area inside the sheath on the wafer, and, consequently, the state of the plasma on the wafer will be uneven, and, as illustrated in FIG. 10, the etching rate becomes locally so high in the portion where a magnetron discharge 61 is generated. Thus, there is a drawback of being unable to have a uniform distribution of the etching rate over the full area on the wafer.
As a method in the attempts of resolving such a drawback and accomplishing a uniform treatment, there is one which is disclosed in U.S. Pat. No. 4,526,643, wherein a plurality of magnets is arranged as to form an endless track and moved in one direction along the endless track, or one which is disclosed in U.S. Pat. No. 4,552,639, wherein the magnetic source consisting of a plurality of permanent magnets radially oriented is eccentrically rotated.
Notwithstanding, there is remained a second drawback that is damaging of the semiconductor device by charged particles, especially by ions. The efficiency of utilization of the applied electric power is so high in the magnetron discharge that the discharge can be maintained by a low voltage, and, consequently, the voltage in the sheath may be made low. Hence, an injection energy of ions in their injection onto the wafer becomes low, and, accordingly, the resultant damaging is said to be low. But, as described in Japanese Patent Publication No. 9394/1986, if an aluminum material is etched, there occurs an objectionable problem that part of the patterns of aluminum, which is covered with a resisting mask and on which etching is not normally done, is destroyed together with the resisting mask.
Generally, the aluminum material is to have layers formed on the Si wafer via SiO.sub.2 of an insulation layer. In the magnetron discharge, a potential difference inside the sheath is so high as some hundreds of volt, and a kinetic energy of electrons performing the cycloidal motion inside the sheath reaches more than 100 eV, which is a relatively high level of energy with reference to the level of 10-20 eV for the primary ionization. Owing to this, in the magnetron discharge, electrons having such a high level of energy collide with the molecules of a treating gas so frequently that the association of the molecules will be dissolved. When BCl.sub.3 is used as a treating gas, for example, it is ionized into molecules such as BCl.sub.2.sup.+ in case of the reactive ion etching (termed hereinafter as `RIE`) while the same is dissociated into atoms such as B.sup.+ +3Cl.sup.+, generating a large number of ions, in case of the magnetron discharge. Hence, in the magnetron discharge, the quantity of ions to be injected on the wafer will become large and they are charged up on the photoresist, and this is considered to destroy part of the aluminum patterns together with the resist. In this way, in the magnetron discharge, ions as dissociated in the form of atoms are generated in large quantities and those ions are injected on the wafer. Therefore, the ions having a greater injection energy and a larger quantity of electric charge, in comparison with the quantity of molecules required for the reaction, will be imposed on the wafer, and this gives rise to a problem of damaging the wafer electrically as well as physically.
Thus, in the magnetron discharge, there has been the drawback of damaging the wafer even after the above referred means for accomplishing good uniformity of the treatment have been put in practice, with a difficulty of achieving a uniform treatment without damaging the wafer.